This invention pertains to fiber optical connectors, and more particularly, to an alignment ferrule for a fiber optical connector made from injection molded plastic and bonding of the fiber to the ferrule using an anaerobic adhesive to quickly bond the fiber and leave a smoothly polished end surface on the ferrule. In other aspects, this invention pertains to a method of terminating a fiber optical connector using an injection molded plastic ferrule with a raised pedestal at one end.
It is known in the art to make a fiber optical connector by securing a fiber optic cable to a ceramic or plastic ferrule. The ferrule is generally cylindrical and has an opening extending therethrough. The opening has a diameter slightly larger than the diameter of the fiber. The fiber, which protrudes from an end of the cable, is inserted through the opening in the ferrule. Generally, bonding of the fiber to the ferrule using adhesives does not occur until the connector is placed in an oven for curing. It is also known in the an to use mechanical and adhesive bonding techniques. Mechanical crimping of the optical fiber cable to a connector does not provide for the precise positioning and bonding of the fiber to the ferrule.
Adhesive compositions have been used and designed specifically for ceramic ferrules but require extended curing times. For example, thermoplastic resins and epoxy are known for bonding to ceramic ferrules. An adhesive, such as epoxy, is introduced into the opening in the ferrule. Epoxy is usually injected into the rear ferrule body and through the ferrule to the ferrule end surface. The bare fiber protruding from the end of a cable is inserted into the rear of the ferrule body and through the opening in the ferrule until it extends from the end surface of the ferrule. The epoxy bonds the fiber to the ferrule after being cured in an oven for approximately ten to twenty minutes and allowed to cool for approximately three minutes. The end of the fiber protruding from the ferrule and the epoxy is then cleaved using cleaving tool. Epoxy surrounding the fiber adjacent the end of the ferrule causes difficulty in locating the cleave position. The fiber is cleaved as close as possible to the end surface without causing cracking of the fiber below the end surface of the ferrule. The epoxy surrounds the fiber sticking out from the end surface of the ferrule in a manner making the fiber susceptible to cracking upon cleaving. The fiber could undesirably shear below the end surface of the ferrule due to the resiliency of the epoxy bead. Polishing the end of the ferrule to bring the fiber to the end surface can be difficult and often results in undesirably polishing away more ferrule than is needed or desired. As the epoxy bead is cured to a hard state an abrasive 12 micron grit polishing lapping film of aluminum oxide must be used to remove the epoxy bead. Such a process may cause over polishing at the end face, causing the fiber to be attenuated. Epoxy beads have been known to shear away from the ferrule end surface during polishing. The fiber might undesirably break below the end surface of the ferrule or crack. Since it is difficult to predict how the fiber will be severed after it is cleaved, proper polishing of the ferrule end is a problem, unless extremely careful polishing methods are followed.
The cost of the ceramic material in a ferrule and the processing of same is considerably more than the cost of a plastic ferrule and its processing, hence, it would be desirable to utilize a relatively inexpensive plastic. Further, it is desired to automate the process of assembling an optical fiber to a ferrule. Present ferrules of either ceramic or plastic do not have a relatively fixed point of extension of the fiber from the ferrule during assembly and thus do not lend themselves readily to automation.
Accordingly, it is an object of the present invention to provide a molded plastic fiber optic ferrule having a pedestal at one end which is easily terminated.
A further object of the present invention is to provide a method of terminating a molded plastic ferrule for a fiber optic connector quickly and inexpensively and which overcomes disadvantages and deficiencies of prior ferrules and bonding techniques.
Another object of the present invention is to provide a method of terminating a molded plastic ferrule for a fiber optic connector using an adhesive for bonding specifically with plastic to achieve a cleanly and securely bonded fiber having attenuation equivalent to ceramic ferrules.
A further object of the present invention is to provide a ferrule which provides for quick and easy polishing and removal of the fiber.
Yet another object of this invention is to provide a molded plastic 2.5 mm ferrule for a fiber optic connector having a raised pedestal adjacent one end surrounding the fiber, for facilitating manufacture of the ferrule with a uniformly polished end surface. Other objects and advantages of this invention will be made more apparent hereinafter.